The invention relates to random access memory for data storage. More specifically, the invention relates to a magnetic random access memory device including an array of memory cells and a write circuit for the memory cells.
Magnetic Random Access Memory ("MRAM") is a type of non-volatile memory that is being considered long term data storage. Accessing data from MRAM devices would be orders of magnitude faster than accessing data from conventional long term storage devices such as hard drives. Additionally, the MRAM devices would be more compact and would consume less power than hard drives and other conventional long term storage devices.
A typical MRAM device includes an array of memory cells. Word lines extend along rows of the memory cells, and bit lines extend along columns of the memory cells. Each memory cell is located at a cross point of a word line and a bit line. A memory cell stores a bit of information as an orientation of a magnetization. The magnetization orientation of each memory cell assumes one of two stable orientations at any given time. These two stable orientations, parallel and anti-parallel, represent logic values of "0" and "1." The magnetization orientation of a selected memory cell may be changed by supplying currents to a word line and a bit line crossing the selected memory cell. The currents create two orthogonal magnetic fields that, when combined, switch the magnetization orientation of a selected memory cell from parallel to anti-parallel or vice versa.
When a memory cell is selected, all of the memory cells along the word line crossing the selected memory cell will see one of the two magnetic fields, and all of the memory cells along the bit line crossing the selected memory cell will see the other of the two magnetic fields. Those memory cells seeing one of the two magnetic fields will hereinafter be referred to as "half-selected" memory cells. Magnetization polarization of all of the half-selected memory cells should be unaffected when a selected memory cell is switched. Otherwise, information stored in half-selected memory cells will be inadvertently erased as bits are written to selected memory cells. In practice, however, switching of the half-selected memory cells can occur. Thus, reliability of storing data in the MRAM device can become a problem.
This problem with the inadvertent switching of half-selected memory cells can become greater as memory cell size is reduced. Thus, reliability of an MRAM device can be further reduced as memory cell size is further reduced. Yet it is always a goal of the industry to reduce cell size to increase memory density. Increasing memory density reduces MRAM cost and size. Suppressing the inadvertent switching of half-selected memory cells would allow cell size to be further reduced.
Therefore, a need exists to suppress the inadvertent switching of half-selected memory cells of MRAM devices.